Wafer support system

ABSTRACT

A wafer support system comprising a segmented susceptor having top and bottom sections and gas flow passages therethrough. A plurality of spacers projecting from a recess formed in the top section of the susceptor support a wafer in spaced relationship with respect to the recess. A sweep gas is introduced to the bottom section of the segmented susceptor and travels through the gas flow passages to exit in at least one circular array of outlets in the recess and underneath the spaced wafer. The sweep gas travels radially outward between the susceptor and wafer to prevent back-side contamination of the wafer. The gas is delivered through a hollow drive shaft and into a multi-armed susceptor support underneath the susceptor. The support arms conduct the sweep gas from the drive shaft to the gas passages in the segmented susceptor. The gas passages are arranged to heat the sweep gas prior to delivery underneath the wafer. Short purge channels may be provided to deliver some of the sweep gas to regions surrounding the spacers to cause a continuous flow of protective purge gas around the spacers. A common bottom section may cooperate with a plurality of different top sections to form segmented susceptors suitable for supporting various sized wafers.

RELATED APPLICATIONS

[0001] This application is a continuation of copending application Ser.No. 09/932,795 filed Aug. 17, 2002, which is a divisional of applicationSer. No. 09/605,094 filed Jun. 27, 2000, now U.S. Pat. No. 6,343,183,which is a divisional of application Ser. No. 08/923,241 filed Sep. 4,1997, now U.S. Pat. No. 6,113,702, which claims the priority benefit ofProvisional application 60/039,850 filed Mar. 5, 1997 and is acontinuation-in-part of abandoned application Ser. No. 08/788,817 filedJan. 23, 1997, which is a continuation-in-part of application Ser. No.08/706,069 filed Aug. 30, 1996, now U.S. Pat. No. 6,053,982, whichclaims the priority benefit of Provisional Application No. 60/003,132,filed Sep. 1, 1995.

FIELD OF THE INVENTION

[0002] The present invention relates to supports for wafers insemiconductor processing chambers and, more particularly, to a systemfor supporting a wafer above a susceptor within a chemical vapordeposition chamber.

BACKGROUND OF THE INVENTION

[0003] High-temperature ovens, or reactors, are used to processsemiconductor wafers from which integrated circuits are made for theelectronics industry. A circular wafer or substrate, typically made ofsilicon, is placed on a wafer support called a susceptor. Both the waferand susceptor are enclosed in a quartz chamber and heated to hightemperatures, such as 600° C. (1112° F.) or higher, frequently by aplurality of radiant lamps placed around the quartz chamber. A reactantgas is passed over the heated wafer, causing the chemical vapordeposition (CVD) of a thin layer of the reactant material on the wafer.Through subsequent processes in other equipment, these layers are madeinto integrated circuits, with a single layer producing from tens tothousands of integrated circuits, depending on the size of the wafer andthe complexity of the circuits.

[0004] If the deposited layer has the same crystallographic structure asthe underlying silicon wafer, it is called an epitaxial layer. This isalso sometimes called a monocrystalline layer because it has only onecrystal structure.

[0005] Various CVD process parameters must be carefully controlled toensure the high quality of the resulting semiconductor. One suchcritical parameter is the temperature of the wafer during theprocessing. The deposition gas reacts at particular temperatures anddeposits on the wafer. If the temperature varies greatly across thesurface of the wafer, uneven deposition of the reactant gas occurs.

[0006] In certain batch processors (i.e., CVD reactors which processmore than one wafer at a time) wafers are placed on a relativelylarge-mass susceptor made of graphite or other heat-absorbing materialto help the temperature of the wafers remain uniform. In this context, a“large-mass” susceptor is one which has a large thermal mass relative tothe wafer. Mass is equal to the density times volume. The thermal massis equal to mass times specific heat capacitance.

[0007] One example of a large-mass susceptor is shown in U.S. Pat. No.4,496,609 issued to McNeilly, which discloses a CVD process wherein thewafers are placed directly on a relatively large-mass, slab-likesusceptor and maintained in intimate contact to permit a transfer ofheat therebetween. The graphite susceptor supposedly acts as a thermal“flywheel” which transfers heat to the wafer to maintain its temperatureuniform and relatively constant. The goal is to reduce transienttemperature variations around the wafer that would occur without the“flywheel” effect of the susceptor.

[0008] In recent years, single-wafer processing of larger diameterwafers has grown for a variety of reasons including its greaterprecision as opposed to processing batches of wafers at the same time.Although single-wafer processing by itself provides advantages overbatch processing, control of process parameters and throughput remainscritical. In systems in which the wafer is supported in intimate contactwith a large-mass, slab-like susceptor, the necessity of maintaininguniform susceptor temperature during heat-up and cool-down cycleslimited the rate at which the temperature could be changed. For example,in order to maintain temperature uniformity across the susceptor, thepower input to the edges of the susceptor had to be significantlygreater than the power input to the center due to the edge effects.

[0009] Another significant problem faced when attempting to obtainhigh-quality CVD films is particulate contamination. One troublesomesource of particulates in the CVD of metals and other conductors is thefilm that forms on the back side of the wafer under certain conditions.For example, if the wafer back side is unprotected or inadequatelyprotected during deposition, a partial coating of the CVD material formsthereon. This partial coating tends to peel and flake easily for sometypes of materials, introducing particulates into the chamber duringdeposition and subsequent handling steps. One example of protecting theback side of a wafer during processing is given in U.S. Pat. No.5,238,499 to van de Ven, et al. In this patent an inert gas isintroduced through a circular groove in the peripheral region of asupport platen. In U.S. Pat. No. 5,356,476 to Foster, et al., asemiconductor wafer processing apparatus is shown, including a pluralityof ducts for introducing helium or hydrogen around the perimeter of awafer to prevent flow of reactant gases downwardly into a gap betweenthe perimeter of the wafer and a wafer support lip. The aforementioneddevices, however, share the feature of rather large wafer supportplatens, characterized by the aforementioned detrimental high thermalmass.

[0010] Presently, there is a need for an improved wafer support systemwhile ensuring temperature uniformity across the wafer surface.

SUMMARY OF THE INVENTION

[0011] The present invention embodies a susceptor which supports a waferspaced therefrom and effectively decouples conductive heat transferbetween the two elements. The wafer is supported on one or more spacersin a recess preferably in an upper surface of the susceptor, the topplane of the wafers preferably being approximately level with an outerledge of the susceptor. In one arrangement, spacer pins are utilized,and in another a single spacer ring is used. The susceptor preferablyincludes a plurality of interior passages opening into the recess at aplurality of small sweep gas holes. A sweep gas flows through thesusceptor and out the holes and protects the back side of the wafer fromdeposition gas and particulate contamination. The sweep gas is heated asit flows through the susceptor so as not to cause localized cooling ofthe wafer and possible areas of slip.

[0012] In one embodiment, the susceptor is formed by top and bottommating sections and the internal passages are formed by grooves in oneof the juxtaposed surfaces of the two sections. Desirably, a multi-armedmember supports and rotates the susceptor, the member preferably beingsubstantially transparent to radiant energy. The arms of the supportmember are preferably hollow and deliver sweep gas to the lower surfaceof the susceptor at apertures in communication with the internalpassages. Some of the sweep gas may be diverted to exit the susceptorproximate the spacer pins to provide sweep gas protection therearound atall times.

[0013] In another aspect of the invention the spacer ring mentioned islocated to be positioned beneath the periphery of the wafer and servesto reduce the size of the sweep gas outlet from beneath the wafer and toblock deposition gas from flowing to the wafer backside. The ring isconfigured to support the wafer in one arrangement. Preferably, the ringand the susceptor are configured to form sweep gas outlet passages. Asanother embodiment, the ring is spaced slightly from the wafer toprovide a thin annular outlet for the sweep gas, and the wafer issupported by pins.

[0014] In one aspect, the invention provides a susceptor to bepositioned in a high temperature processing chamber for supporting awafer to be processed. The susceptor includes a thin, substantially discshaped lower section and a thin, substantially disc shaped upper sectionhaving a lower surface in engagement with an upper surface of said lowersection. One of the sections has an outer diameter larger than that ofthe other section, the larger section having a recess in which the othersection is positioned. One or more gas channels are defined by theengaging surfaces of the sections. The susceptor includes one or moregas inlets in the lower section opening to its lower surface and thechannels. One or more gas outlets in the upper section open to the uppersurface of the upper section in an area beneath that in which a wafer tobe processed is to be positioned. The mating recess is preferably formedin a lower surface of the upper section. In one form, the channels areformed by grooves in the upper surface of the lower section with thegrooves being closed by the lower surface of the upper section. Thereare preferably three of the inlets each opening to the channels, thechannels being interconnected to allow gas flow throughout.

[0015] In accordance with another aspect, the invention provides anapparatus for chemical vapor deposition on a semiconductor wafercomprising a deposition chamber having a process gas inlet for injectingprocess gases into the chamber. A single susceptor is provided in thechamber. A support for the susceptor includes a central shaft positionedbelow the susceptor axis and a plurality of support arms extendingradially and upwardly from the shaft with the arms having upper endsadapted to engage the lower surface and support the susceptor. One ormore of the arms are tubular and in registry with inlets in thesusceptor so that gas may be conducted through the tubular arms into theinlets.

[0016] The present invention also provides a method of supporting asemiconductor wafer in a processing chamber and conducting gas flowbeneath the wafer. The method comprises the steps of positioning thewafer on a plurality of spacers protruding upwardly from an uppersurface of the susceptor to support the wafer and form a gap between thewafer and the upper surface of the susceptor. The susceptor is supportedon a plurality of arms having upper ends engaging a lower surface of thesusceptor. Gas flows through one or more of the arms into passages inthe susceptor which open to the gap. The gas is allowed to flowoutwardly beyond the periphery of the wafer. Desirably, the spacers arepositioned in apertures in the susceptor, and some of the gas flows fromthe arms through the susceptor passages and into the gap via theapertures surrounding the spacers.

[0017] In another aspect of the invention, an apparatus for supportingwafers in a semiconductor processing environment includes a lowersection and a plurality of disk-shaped upper sections each adapted toregister concentrically with the lower section. The upper sections eachhave a shallow wafer recess sized differently than the other uppersections to enable selection of the upper section depending on the sizeof wafer to be processed. The apparatus preferably includes at least twoupper sections for processing wafers having diameters greater than 100mm.

[0018] In a preferred form of the invention, a rotatable susceptor ispositioned generally horizontally in a processing chamber and one ormore spacers extend above the susceptors to support a single waferspaced from the susceptor. A temperature compensation ring surrounds butis slightly spaced from the susceptor and has a generally rectangularexterior shape. The chamber has at least one process gas inlet and atleast one gas outlet for flowing deposition and carrier gas across theupper surface of the wafer, and the chamber has a generally rectangularcross-section generally perpendicular to the gas flow across the waferand the rectangular ring. An inlet section of the chamber is verticallyshort and the susceptor and the ring are positioned adjacent the inletsection with the upper surface of the ring and the susceptor beinggenerally in the plane of the lower wall of the inlet section. The ringand the susceptor, together with a wafer mounted on the spacers areheated very uniformly by upper and lower heat sources. With thisarrangement, the gas has a generally uniform flow across the width ofthe chamber since deposition occurs on both the heated ring and thewafer. As a result, carrier gas flow is advantageously reduced from thatneeded with a circular susceptor and a circular temperature compensationring wherein it is usually necessary to have increased process gas flowacross the center of the wafer and reduced flow across the edges of thewafer in order to obtain uniform deposition on the wafer. The reducedcarrier gas flow is particularly desirable because of the reducedcooling effect on the thermally sensitive wafer spaced from thesusceptor. It is also desirable that the upper and lower heat sourceshave a generally rectangular heat pattern that coincides with the shapeof the exterior of the rectangular ring so that the heat is principallydirected to the area defined by the ring exterior.

[0019] In another aspect of the invention the system is provided withthe capability to modify the ratio of heat provided by upper and lowerheat recesses during the processing of a wafer, so as to promote rapiduniform heating.

[0020] With the wafer no longer in contact with the susceptor, the wafertemperature can be maintained uniform even where the susceptorexperiences temperature non-uniformities during heat-up and cool-down.In this manner, heat-up and cool-down times can possibly be reduced.Process throughput is thereby increased, as desired. Another aspect ofthe invention allows for the processing of wafers without the creationof haze or other undesirable effects on the underside of the wafer. Thisimprovement, provided by removing the wafer from contact with thesusceptor and bathing its underside with a gas, e.g. hydrogen, isparticularly important where double-sided polished wafers are beingprocessed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a cross-sectional view along the longer of twohorizontal axes through a reactor chamber incorporating an improvedwafer support system of the present invention;

[0022]FIG. 2 is a cross-sectional view through one embodiment of a wafersupport system of the present invention;

[0023]FIG. 2a is a detailed view of one embodiment of a wafer spacer inthe form of a pin;

[0024]FIG. 2b is a detailed view of an alternative wafer spacer in theform of a sphere;

[0025]FIG. 2c is a view of an alternative wafer spacer configuration;

[0026]FIG. 3 is an exploded view of the wafer support system illustratedin FIG. 2;

[0027]FIG. 4 is a top plan view of an upper section of a segmentedsusceptor of the wafer support system taken along line 4-4 of FIG. 3;

[0028]FIG. 5 is a top plan view of a lower section of the segmentedsusceptor taken along line 5-5 of FIG. 3;

[0029]FIG. 6 is a top plan view of a susceptor support for use in thewafer support system of the present invention, taken along line 6-6 ofFIG. 3;

[0030]FIG. 7 is a cross-sectional view of another wafer support systemaccording to the present invention;

[0031]FIG. 8 is a top plan view of a segmented susceptor for use in thewafer support system of FIG. 7, taken along line 8-8;

[0032]FIG. 9 is a top plan view of an alternative upper section of asegmented susceptor having gas outlets distributed around concentriccircles;

[0033]FIG. 10 is a top plan view of an alternative lower section of asegmented susceptor having multiple gas delivery grooves arranged inconcentric circles;

[0034]FIG. 11 is a top plan view of a preferred wafer support system ofthe present invention;

[0035]FIG. 12 is a top plan view of a first version of a top section ofa segmented susceptor for use in the wafer support system of FIG. 11;

[0036]FIG. 13 is a top plan view of a bottom section of the segmentedsusceptor of the wafer support system of FIG. 11;

[0037]FIG. 14 is a cross-sectional view of a captured wafer spacer andpurge channel within the segmented susceptor, taken along line 14-14 ofFIG. 11;

[0038]FIG. 15 is a top plan view of a second version of the top sectionof the segmented susceptor for use in the wafer support system of FIG.11;

[0039]FIG. 16 is a top plan view of a third version of the top sectionof the segmented susceptor for use in the wafer support system of FIG.11;

[0040]FIG. 17 is a top plan view of a fourth version of the top sectionof the segmented susceptor for use in the wafer support system of FIG.11;

[0041]FIG. 18 is a cross-sectional view through another variation of areactor chamber incorporating the wafer support system of the invention;

[0042]FIG. 19 is a top plan view of the chamber of FIG. 18; and

[0043]FIG. 20 is a graph showing changes in lamp power ratio during adeposition cycle.

[0044]FIG. 21A is a top-plan view of the upper segment of anothervariation of segmented susceptor.

[0045]FIG. 21B is a top-plan view of the lower segment of a susceptorwhich mates with the upper segment shown in FIG. 21A, a portion of whichis shown.

[0046]FIG. 21C is a cross-sectional view of the segments of 21A and Bassembled and supporting a wafer.

[0047]FIG. 21D is an enlarged cross-sectional view of one edge of theassembly of FIG. 21C illustrating more clearly the location of a supportpin in reference to a wafer having a notch in its periphery.

[0048]FIG. 21E is a view similar to that of FIG. 21D but illustrating awafer having an edge alignment flat.

[0049]FIG. 22A illustrates a top-plan view of the lower segment ofanother segmented susceptor design with a portion of an upper segmentsuperimposed thereon to illustrate the relationship between the two.

[0050]FIG. 22B is an enlarged cross-sectional view of a portion of theupper and lower segments of FIG. 22A assembled and supporting a wafer.

[0051]FIG. 23A is top-plan view of an upper segment of another susceptorwith a wafer support ring mounted on the upper segment, and with aportion of a lower segment shown.

[0052]FIG. 23B is an enlarged cross-sectional view illustrating therelationship between the wafer support ring of FIG. 23A and a wafer.

[0053]FIG. 23C is an enlarged fragmentary view illustrating thecross-section of the sweep gas passages in the support ring on FIGS. 23Aand 23B.

[0054]FIG. 24 is a plan view of another embodiment of a spacer orblocker ring.

[0055]FIG. 25 is a view taken on line 25-25 of FIG. 24.

[0056]FIG. 25A is a view on line 25A-25A of FIG. 25, with a fragmentary,broken line showing of a susceptor and a wafer.

[0057]FIG. 25B is a view on line 25B-25B of FIG. 25.

[0058]FIG. 25C is a view on line 25C-25C of FIG. 25.

[0059]FIG. 26 is a plan view of another embodiment of a blocker ring.

[0060]FIG. 27 is a view on line 27-27 of FIG. 26.

[0061]FIG. 27A is a view on line on line 27A-27A of FIG. 27, with afragmentary, broken line showing of a susceptor and a wafer.

[0062]FIG. 27B is a view on line 27B-27B of FIG. 27.

[0063]FIG. 27C is a cross-sectional view of a variation of the ring ofFIG. 27B.

[0064]FIG. 27D is an enlarged view of the area identified by circle 27Dshown on FIG. 27B.

[0065]FIG. 28 is a cross-sectional view of an alternative blocker ringconfiguration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0066]FIG. 1 illustrates a reactor chamber 20 for processingsemiconductor wafers, within which a wafer support system 22 of thepresent invention is incorporated. Prior to discussing the details ofthe wafer support system 22, the elements of the reaction chamber 20will be described. The support system is suitable for many types ofwafer processing systems, another one being shown in FIGS. 18 and 19,and the discussion herein should not be limited to one particular typeof reaction chamber.

[0067] The chamber 20 comprises a quartz tube defined by an upper wall24, a lower wall 26, an upstream flange 28, and a downstream flange 30.Although not shown in the figure, the walls have a concave inner surfaceand a convex outer surface which, when viewed from a lateralcross-section, has a lenticular shape; and lateral edges of the reactionchamber 20 include relatively thick side rails between which a chambersupport plate 32 is attached. FIG. 1 is a longitudinal cross-sectionalong a central vertical plane of the chamber 20 illustrating thevertical dimension of the lenticular shape; the side rails are thus notseen. Preferably, the chamber 20 is manufactured from quartz. Thechamber support plate 32 reinforces the chamber 20 during vacuumprocessing and extends between the side rails (not shown), preferablyalong the center line of the chamber 20. The support plate 32 includesan aperture 33 defining a void or opening 35 extending across thelateral dimension of the chamber 20 between the side rails. The aperture33 divides the support plate 32 into an upstream section extending fromthe upstream flange 28 to an upstream edge of the aperture, and adownstream section extending from a downstream of the aperture to thedownstream flange 30. The upstream section of the support plate 32 ispreferably shorter in the longitudinal direction than the downstreamsection.

[0068] An elongated tube 34 depends from a centrally located region ofthe lower wall 26. A drive shaft 36 extends through the tube 34 and intoa lower region 38 of the chamber 20. The lower region 38 is definedbetween the central chamber support plate 32 and the lower wall 26. Theupper end of the drive shaft 36 is tapered to fit within a recess of amulti-armed support or spider assembly 40 for rotating a segmentedsusceptor 42. The susceptor 42 supports a wafer 44, shown in phantom. Amotor (not shown) drives the shaft 36 to, in turn, rotate the wafersupport system 22 and wafer 44 thereon within the aperture 33. A gasinjector 46 introduces process gas, as indicated by arrow 48, into anupper region 50 of the chamber 20. The upper region 50 is definedbetween the upper wall 24 and the chamber support plate 32. The processgas passes over the top surface of the wafer 44 to deposit chemicalsthereon. The system typically includes a plurality of radiant heat lampsarrayed around the outside of the reaction chamber 20 for heating thewafer 44 and catalyzing the chemical deposition thereon. An upper bankof elongated heat lamps 51 is illustrated outside of the upper wall 24,and typically a lower bank of lamps arranged cross-wise to the upperbank is also utilized. Further, a concentrated array of lamps directedupward from underneath the susceptor 42 is often used.

[0069] A source of sweep gas 37 is schematically shown connected througha mass flow controller 39 to the drive shaft 36. Gas flows into thespace within the hollow shaft 36 and is eventually directed upwardthrough the susceptor 42, as will be more fully described below. Thefluid coupling allowing gas to the interior of the hollow, rotatingshaft 36 is not shown, but may accomplished by a number of means, one ofwhich is shown and described in U.S. Pat. No. 4,821,674, issued Apr. 18,1989, hereby expressly incorporated by reference.

[0070] A wafer is introduced to the reaction chamber 20 through a waferentry port 47. The wafer is typically transported by a robot pick-up arm(not shown) which enters through the port 47 and extends over the wafersupport system 22 to deposit the wafer thereon. The CVD system thenseals the reaction chamber 20 and introduces deposition gas with acarrier gas such as hydrogen for depositing a layer of silicon or othermaterial on the wafer. After processing, a gate valve opens and therobot pick-up arm enters through the port 47 and retracts the wafer fromthe susceptor 42. Periodically, the reaction chamber 20 must beconditioned for subsequent processing. A typical sequence is theintroduction of an etch gas into the reaction chamber with the gatevalve closed to clean any particular deposition from the interior walls.After the etching, a silicon precursor is sometimes introduced into thechamber to provide a thin coat of silicon on the susceptor 42. Such acoating step is sometimes termed capping. After the etching and cappingsteps, the chamber is purged with hydrogen and heated for introductionof the next wafer.

[0071] The tube 34 is sized slightly larger than the drive shaft 36 toprovide space therebetween through which purge gas 52 flows. The purgegas enters the lower region 38 of the reaction chamber 20 to helpprevent reactant gas from depositing in the lower region. In thisrespect, the purge gas 52 creates a positive pressure below the wafersupport system 22, which helps prevent reactant gas from travelingaround the sides of the segment susceptor 42 in the lower region 38. Thepurge gas is then exhausted, as indicated with arrows 55, between thesusceptor 42 and aperture 33 into the upper region 50 and then throughan elongated slot 60 in the downstream flange 30. This ensures thatreactant gases do not migrate into the lower region 38. The purge gascontinues through an exhaust system 58. The reactant gas likewise passesthrough the elongated slot 60 in the downstream flange 30 to be ventedthrough the exhaust system 58.

[0072] Preferably, a temperature compensation ring 62 surrounds thewafer support system 22. The ring 62 fits in the opening 35 created bythe aperture 33 in the support plate 32, and the wafer support system 22and ring substantially fill the opening and provide structure betweenthe lower and upper chamber regions 38, 50. The susceptor 42 rotateswithin the ring 62 and is preferably spaced therefrom across a smallannular gap of between 0.5 and 1.5 millimeters. The shape of theaperture 33 in the support plate 32 surrounding the ring 62 can be madecircular so that the edges of the opening 35 are in close proximity tothe ring. However, it has been found that a generally rectangularaperture 33 is preferred. In this respect, the ring 62 may have agenerally rectangular outer periphery, or a second structure may beutilized to fill the gap between the circular ring and the aperture 33.As will be described in greater detail below, the susceptor 42 ispreferably manufactured to have a constant outer diameter to fit withinthe ring 62, and surrounding aperture 33. Although the susceptor 42 hasa constant outer diameter, it will be seen that various configurationsare provided for processing a number of different size wafers.

[0073] In a particularly advantageous embodiment, the temperaturecompensation ring 62 comprises a two-part structure circular ring havinga cavity therein for receiving thermocouples 64. In the embodimentshown, the thermocouples 64 enter the chamber 20 through aperturesformed in the downstream flange 30 and extend underneath the supportplate 32 into the temperature compensation ring 62. The apertures in thequartz flange 30 substantially prevent gas leakage around thethermocouples 64, although typically no additional seal is used. Thereare preferably three such thermocouples, one terminating at a leadingedge 66, one terminating at a trailing edge 68, and one terminating ateither of the lateral sides of the ring 62. The thermocouples within thering 62 surrounding the segmented susceptor 42 provide good temperatureinformation feedback for accurate control of the radiant heating lamps.A plurality of bent fingers 70 attached to the support plate 32 supportthe ring 62 around the periphery of the susceptor 42. In addition to thering 62 and thermocouples therein, a central thermocouple 72 extendsupward through the drive shaft 36, which is hollow, and through thespider assembly 40 to terminate underneath the center of the susceptor42. The central thermocouple 72 thus provides an accurate gauge of thetemperature near the center of the wafer 44. Because the temperature ofa wafer changes quickly in the present system, it is desirable that themass of the thermocouples be minimized to speed response time.

[0074] Referring to FIG. 2, a first embodiment of a wafer support system22 is shown. Again, the system 22 generally comprises the segmentedsusceptor 42 supported by arms 74 of the spider assembly 40. The arms 74extend radially outward from a hub 76 and bend vertically upward atpredetermined radial distances to contact the underside of the susceptor42. The segmented susceptor 42 comprises an upper section 78 and a lowersection 80, both sections being generally planar disk-shaped elements.Both sections 78, 80 of the susceptor 42 are preferably machined out ofgraphite and fit closely together without additional fastening means toensure minimal gas leakage therebetween. A gap of less than 0.001 inchbetween the adjacent circular surfaces of the upper and lower sections78, 80 is acceptable for this purpose. A thin coating of silicon carbidemay be formed on one or both sections 78, 80. The thickness of thesusceptor 42 is preferably about 0.30 inches.

[0075] With reference to the exploded view of FIG. 3, the upper section78 generally comprises an outer ring 82 surrounding a thinner circularmiddle portion. The outer ring 82 comprises an upper rim or ledge 84 anda lower rim or skirt 86 which terminate at upper and lower shoulders orsteps 88, 90, respectively. The upper step 88 forms a transition betweenthe ledge 84 and a circular wafer-receiving recess 92. The lower step 90forms a transition between the skirt 86 and an annular recess 94 in theunderside of the upper section 78. The upper section 78 further includesa circular pattern of sweep gas outlets 96 symmetrically disposed aboutthe central axis of the upper section, and in the recess 92.

[0076] At spaced locations distributed around a circle concentric aboutthe axis of the susceptor 42, a plurality of counter-bored holes 98 areformed proximate the upper step 88. The counter-bored holes 98 include asmaller through hole opening to the circular recess 42 and a largercounterbore concentric with the smaller through hole and openingdownwardly to the annular recess 94. Each counter-bored hole 98 is sizedto receive a wafer support or spacer 100 which projects into thecircular recess 92. The wafer 44 rests on the spacers 100 above thefloor of the recess 92. In this respect, the recess 92 is sized toreceive a wafer therein so that the edge of the wafer is very close tothe step 88. The upper section 78 further includes a downwardlydepending central spindle 102 defining a radially inner border of theannular recess 94. A central thermocouple cavity 104 is defined in thespindle 102 for receiving a sensing end of the central thermocouple 72previously described.

[0077] With reference to FIGS. 3 and 5, the annular lower section 80comprises a central through bore 106 sized to fit around the downwardlydepending spindle 102 of the upper section 78. The upper surface of thelower section 80 includes a plurality of gas passage grooves. Morespecifically, a pattern of curvilinear distribution grooves 108 extendbetween a plurality of gas flow passages 110 and a central circulardelivery groove 112. Each of the grooves 108 and 112 is generallysemicircular in cross section and has a depth approximately equal tohalf the thickness of the lower section 80. Each of the gas flowpassages 110 opens downwardly into shallow spider arm cavities 114.

[0078] With reference to FIGS. 3 and 6, the spider assembly 40 isdescribed in more detail. The central hub 76 comprises a generallyhollow cylindrical member having a vertical through bore extending froma lower surface 116 to an upper surface 118. The through bore comprisesa lower shaft-receiving tapered portion 120, a central gas plenum 122,and an upper thermocouple channel 124. The lower tapered portion 120receives the tapered upper end of the hollow drive shaft 36, the twoelements having identical taper angles to fit snugly together. Thethermocouple channel 124 receives the central thermocouple 72 whichextends upward into the thermocouple cavity 104 in the upper section 78of the segmented susceptor 42. The gas plenum 122 includes a pluralityof apertures 126 aligned with each of the support arms 74. In thisrespect, the support arms are hollow, with an interior defining sweepgas passages 128. The upwardly directed terminal ends of the arms 74 arereinforced by annular lips 130. The lips 130 are sized to fit closelywithin the shallow arm-receiving cavities 114 in the underside of thelower section 80. The shaft 36 rotatably drives the spider assembly 40which, in turn, drives the susceptor 42 by the registration between thelips 130 and the shallow cavities 114 in the underside of the lowersection 80.

[0079] In an alternative embodiment, the curved arms of the spiderassembly 40 may be replaced by a pair of perpendicularly disposed tubes.That is, for each of the three arms, a first tube may extend radiallyoutward from the central hub 76 and couple with a second larger tubeperpendicular thereto and extending upward to fit closely within the armreceiving cavities 114. This arrangement can be visualized somewhat likea corncob pipe. The first tubes of each arm may radiate horizontallyfrom the hub 76 or may be slightly upwardly angled. Utilizing straightcylindrical sections, rather than a curved quartz tube, is lessexpensive to manufacture.

[0080] Referring back to FIG. 2, the spacers 100 may take severalshapes. In one preferred embodiment, seen in detail in FIG. 2a, thespacer 100 is in the form of a pin comprising an elongated upper portion132 having a small rounded head. A base 134 sized larger than theelongated portion 132 fits within the counter-bored hole 98. The base134 rests on the upper surface of the lower section 80. The heads of theelongated portions 132 of the multiple spacers 100 terminate at the sameheight to provide a planar support surface for the wafer 44. The upperportion of the counter-bored holes 98 is approximately 0.062 inches indiameter and the spacers 100 fit therein. The spacers 100 shouldpreferably space a wafer above the recess in a range of about 0.010 toabout 0.200 inches; or more preferably in a range of about 0.060 toabout 0.090 inches; and most preferably the spacers 100 support thewafer 44 over the floor of the recess, a height of about 0.075 inches.This is about three times the thickness of a typical wafer. This spacingis significantly greater than the deviation from flatness of thesusceptor or wafer which is in the order of 0.005-0.010 inches. Also thespacing is much greater than the depth of a grid on the upper surface ofa prior art susceptor which had been designed to optimize thermalcontact between the susceptor and wafer while also facilitating waferpickup. In a preferred embodiment, the depth of the recess 92 and spacer100 height is such that the top surface of the wafer 44 is in the planeof the outer ledge 84 to minimize any irregularity or transition andsmooth gas flow thereover. Alternatively, the ledge 84 might be formedabove or below the top of the wafer 44 as desired.

[0081] In an alternative embodiment, seen in FIG. 2b, the spacer 100takes the form of a sphere 136 which fits within a cradle 138 formed inthe upper surface of the upper section 78. The spacer 100 may even beformed integrally in the upper section 78. Desirably, the upper wafercontacting portion of the spacer 100 is rounded or terminates in a pointto minimize contact area with the wafer.

[0082]FIG. 2c, however, illustrates an alternative pin headconfiguration that is useful with systems in which the wafer is droppeda short distance when being placed on the pins. That is, in one wafertransport system, the wafer is held by use of a so-called Bernoulli wandwherein a wafer is held from above by radially outward gas flow, withoutthe wafer upper surface being touched by the wand. After a wafer ismoved into position slightly above a susceptor, the gas flow isinterrupted and the wafer falls onto the spacers. While the falldistance is very slight, there is some possibility of a spacer pin withpoint contact chipping or marring the surface of the wafer contactingthe spacer. To minimize that possibility, the pin head of FIG. 2c has aflat upper surface 139 with rounded shoulders 139 a. Preferably, thediameter of the flat area is in the range of about 0.025″ to 0.045″, orthe entire upper surface of about 0.055″ could be flat. It is alsodesirable that the flat surface 139 be polished to remove roughness onthe surface that could possibly damage the wafer.

[0083] The fixed spacers 100 define a planar support platform or standfor the wafer 44 to space the wafer above the segmented susceptor 42,and in this respect at least three spacers are required, although morethan three may be provided. Preferably, the spacers 100 are manufacturedof a ceramic or naturally occurring or synthetically fabricatedsapphire, sapphire being a single crystal structure derived fromaluminum oxide. In an alternative configuration, the spacers 100 may beformed of amorphous quartz, although this material may eventuallydevitrify from the repeated thermal cycling within the reaction chamber20. Further materials which may be used for the spacers includemonocrystalline or single crystal quartz, silicon carbide, siliconnitride, boron carbide, boron nitride, aluminum nitride, and zirconiumcarbide, or other high-temperature resistant material capable ofwithstanding the extreme temperatures and the chemical environment inthe wafer processing chamber. Any of these materials may additionally becoated with Si, Si₃N₄, SiO₂ or SiC to protect the spacers fromdeterioration from exposure to process gases.

[0084] To prevent back-side contamination of the wafer 44 from reactantgases entering between the wafer and the susceptor 42, a novel sweep gassystem is provided. The system also preheats the gas which contacts thewafer and which if not heated would cause localized cooling and possibleareas of slip on the wafer. More particularly and with reference to FIG.2, the sweep gas enters the wafer support system through the hollowdrive shaft 36 and into the plenum 122, as indicated with arrow 140. Thegas is then distributed through the apertures 126 and into the sweep gaspassages 128 within the arms 74. The gas continues in an inlet flow 142into the gas flow passage 110 through the lower section 80. Thedistribution grooves 108 along with the lower surface of the uppersection define gas channels between the upper and lower sections 78, 80.Referring to FIG. 5, the gas flows along the channels following thevarious distribution grooves 108 to finally reach the circular deliverygroove 112, thereafter exiting through the sweep gas outlets 96, asindicated by arrow 144. The gas flow through the distribution grooves isshown by arrows 146. The gas flow into the delivery groove 112 is shownby arrows 148. The specific arrangement of the distribution grooves 108may be different than that shown in FIG. 5. The arrangement shown helpsreduce temperature nonuniformities through the lower section 80 andthrough the segmented susceptor 42 as a whole by channeling the sweepgas in a circuitous and symmetric path through the lower section.Desirably, the grooves 108 traverse a nonlinear path from the gas flowpassages 110 to the central circular delivery groove 112 and sweep gasoutlets 96.

[0085] The circular delivery groove 112 is formed directly underneaththe circular pattern of sweep gas outlets 96. As seen in FIG. 4, theeven distribution of gas through the groove 112 ensures that the sweepgas flow 148 leaving the outlets 96 is axisymmetric about the center ofthe susceptor 42 in a radially outward direction. In this manner, anyreactant gas which might enter between the wafer and the susceptor isswept radially outward from underneath the wafer. Desirably, a flow rateof less than 5 standard liters/minute of sweep gas through the hollowshaft 36 and segmented susceptor is utilized, and a flow rate of lessthan 3 standard liters/minute is preferred.

[0086] Although other gases may be substituted, hydrogen is preferred asit is compatible with many CVD processing regimes. As a result of theexcellent control over the backside of the wafer through the use of thepurge gas, wafers with double-sided polishing can be processedsuccessfully, unlike a system with the wafer in contact with thesusceptor.

[0087] The present invention includes the mass flow controller 39 toregulate the flow of sweep gas through the hollow shaft 36 and segmentedsusceptor for different processing pressures. That is, some processesare at atmospheric pressure, and some are at reduced pressure. In thecase of a fixed restriction to control flow, a reduced pressure processwill tend to increase the flow of gas through the sweep gas outlets 96as compared to an atmospheric process, all other variables remaining thesame. Thus, the mass flow controller 39 operates independently from theprocess pressure to ensure a constant flow of less than 5 standardliters/minute.

[0088]FIGS. 7 and 8 illustrate another wafer support system 22′ whichutilizes some of the same elements as the wafer support system 22 shownin FIG. 2. More particularly, the spider assembly 40 and lower section80 of the segmented susceptor 42′ are identical to those shown anddescribed with reference to the first embodiment. The segmentedsusceptor 42′, however, includes a modified upper section 78′, with anouter ring 82′ comprising an upper ledge 84′ and a lower skirt 86′. Theupper ledge 84′ is sized similar to the ledge 84 described with respectto the first embodiment and terminates in a circular step 88′ leading toa circular recess 92′. The circular recess 92′ extends radiallyoutwardly past the lower section 80. In relative terms, the lower skirt86′ is substantially greater in the radial dimension in comparison tothe skirt 86 described for the first embodiment, yet the step 90′ issized the same as the step 90 in the first embodiment. This allows theupper section 78 to receive the annular lower section 80 therein, justas in the first embodiment.

[0089] In a departure from the first embodiment, as seen in FIG. 7, thesusceptor 42′ includes a plurality of spacers in the form of supportpins 150 circumferentially distributed about a circle around the centralaxis of the susceptor 42′ in the region between the upper step 88′ andthe lower step 90′. More particularly, the pins 150 extend withinstepped cavities 152, extending through the upper section 78′ from therecess 92′ to the extended skirt 86′. The pins 150 shown are somewhatdifferent than the first two embodiments described with respect to FIGS.2a and 2 b, and comprise simple cylindrical elements having roundedheads in contact with the wafer 44′.

[0090] An alternative embodiment of gas passage grooves through thesusceptor is shown in FIGS. 9 and 10. As before, the spider assembly 40supports a modified susceptor having an upper section 162 and a lowersection 164. The lower section 164 includes three gas passages 166opening downwardly to receive the upper ends of the spider assembly arms74. In this respect, the locations of the sweep gas inputs are in thesame location as with the first two susceptor embodiments 42 and 42′.From there, however, distribution grooves 168 in the upper surface ofthe lower section 164 extend radially outward to an outer circulargroove 170. Secondary grooves 172 channel the sweep gas radially inwardto intersect a series of concentric circular delivery grooves 174 a, 174b and 174 c located at spaced radii. Each secondary groove 172preferably lies along a line which bisects the included angle definedbetween each pair of distribution grooves 168.

[0091] Looking at FIGS. 9 and 10, the upper section 162 includes aplurality of gas outlets arranged in a series of concentric circlescorresponding to the circular delivery grooves 174 a, 174 b and 174 c.More particularly, a first group of outlets 176 a lie along an innercircle 178 a at the same radius of the smallest delivery groove 174 a.Likewise, two more groups of outlets 176 b and 176 c are arranged aboutouter concentric circles 178 b and 178 c, respectively, which correspondto the outer delivery grooves 174 b and 174 c.

[0092] Four outlets 176 are shown distributed evenly about each of thecircles 178 a,b,c, but more or less may be provided. Furthermore, thecircumferential orientation of the outlets 176 may be staggered betweenthe circles 178 as shown. With four outlets 176 per circle 178, eachpattern of outlets is rotated 30□ with respect to one of the otherpatterns. Alternatively, for example, eight outlets 176 per circle 178evenly distributed and staggered would mean that each pattern of outletsis rotated 15□ with respect to one of the other patterns. The staggeringbetween patterns creates a more effective gas sweep under the wafer, asshown by arrows 180, than if the outlets 176 were aligned.

[0093] In another variation, the upper section 162 may be used with thelower section 80 described above with respect to FIGS. 3 and 5 as longas the inner circle 178 a of outlets 176 a aligns with the circulardelivery groove 112. In that case, the outer circles 178 b,c of outlets176 b,c would not be used. Additionally, the lower section 164 may beused with either of the above described upper sections 78, 78′ as longas the inner delivery groove 174 a aligns with the circular pattern ofoutlets 96, 96′. In that case, the outer delivery grooves 174 b,c wouldnot be used. Of course, other variations are contemplated.

[0094] The separation between the wafer 44 and the segmented susceptor42, as well as the minimal direct support provided by the three spacers100, effectively decouples the wafer and susceptor from heat conductiontherebetween. The wafer 44 temperature is thus influenced primarily fromradiant heat flux provided by the lamps surrounding the chamber.

[0095] The spider assembly 40 is preferably constructed of quartz toprovide a transparent support to the underside of the susceptor 42 tominimize the obstruction of radiant heat emitted from the lower heatlamps. Although quartz is preferred, other materials having a relativelyhigh coefficient of radiant heat transmission may be utilized. Toconstruct the spider assembly 40, the hub 76 is first machined into theproper shape. The tubular arms 74 are bent from straight portions andattached to the hub 76 by welding, for example. Heat treating and firepolishing reduce internal stresses in the quartz.

[0096]FIG. 11 illustrates a top plan view of another wafer supportsystem 200 of the present invention again comprising a segmentedsusceptor 202 having a concentric recess 204 in a top surface, and aplurality of wafer support spacers 206 positioned within the recess.

[0097] With reference FIG. 12 which illustrates a top section 208 of thesegmented susceptor 202, the shallow recess 204 is defined around itsouter perimeter by a circular step 210 leading to a ledge 212 whichforms the uppermost surface of the susceptor. The construction is, inmany respects, similar to the susceptors previously described.

[0098] In a departure from the previously described susceptors, thesegmented susceptor 208 includes two concentric circles of sweep gasoutlets. An outer circle of twelve sweep gas outlets 214 surrounds aninner circle of twelve sweep gas outlets 216. It can be readily seenfrom FIG. 12 that the outer sweep gas outlets are distributed about thecenter of the segmented susceptor 208 at intervals of 30°, or at 1:00,2:00, etc. The inner circle of sweep gas outlets 216, on the other hand,are offset 15° rotationally with respect to the outer circle, and thusoccupy rotational positions at 12:30, 1:30, etc., intermediate the outercircle of outlets. This increased number of sweep gas outlets andstaggered relationship of the concentric circles increases theuniformity of sweep gas underneath the wafer and improves performancetherefor; as was previously described with respect to FIG. 9.

[0099]FIG. 11 illustrates in dashed line, an interface 219 between thetop section 208 and a bottom section 218 of the segmented susceptor 202,the bottom section being seen in top plan view in FIG. 13. The outerperiphery of the bottom section 218 is substantially circular, exceptfor three flats 220 disposed at 120° intervals therearound. The outerperiphery of the bottom section 218 fits within a similarly shaped lowerstep 222 of the top section 208, as seen in dashed line in FIG. 12, andin cross-section in FIG. 14. The flats 220 of the bottom section 218cooperate with inwardly-facing flats 224 formed in the lower step 222 torotationally orient the top section 208 with the bottom section 218. Thebottom section 218 further includes a small central through bore 226within which a downwardly depending hub or spindle 228 of the topsection fits.

[0100] The underside of the bottom section 218 includes three shallowspider arm cavities 230, similar to those previously described. Thecavities 230 communicate with vertical gas flow passages 232 leading toa plurality of gas distribution grooves 234 formed in the upper surfaceof the bottom susceptor section 218. As seen in FIG. 13, each gas flowpassage 232 communicates with diverging grooves 234 which travelcircuitous paths extending first radially outwardly, thencircumferentially adjacent the periphery of the susceptor lower section,and finally generally radially inwardly toward the center of the bottomsection 218. In this manner, sweep gas flows substantially through theentire susceptor in a generally axisymmetrical pattern to provide evenheat transfer to the sweep gas from the hot susceptor, and visa versa.

[0101] Both gas distribution grooves 234 intersect a continuous outercircular delivery groove 236 concentrically formed in the bottom section218. From the outer groove 236, a plurality of angled spokes 238 lead toan inner circular delivery groove 240, again concentrically formed inthe bottom section 218. Although the gas distribution grooves 234 areshown continuing directly into each of the spokes 238, otherarrangements are possible. Furthermore, the spokes 238 are shownintersecting the inner circular delivery groove 240 at generallytangential angles, but may also be connected at other more direct radialangles. The gas flow passages 232 are located radially outward from thesweep gas outlets 216 and the gas distribution grooves 234 desirablytraverse a nonlinear path therebetween, preferably longer than a directline between any of the passages 232 and outlets 216, and mostpreferably in a circuitous pattern such as the one shown.

[0102] The inner circular delivery groove 240 lies directly underneaththe inner circle of sweep gas outlets 216 when the top section 208 iscoupled over the bottom section 218. Likewise, the outer circulardelivery groove 236 lies directly underneath the outer circle of sweepgas outlets 214. This arrangement allows for an even pressure and supplyof sweep gas to all of the outlets 214, 216 in the top surface of thesegmented susceptor 208. The pressure created between the top and bottomsections 208, 218, is reduced somewhat from previously describedembodiments by the increase in the number of sweep gas outlets 214, 216,and by the reduction in size of the inlet gas flow passages 232. Morespecifically, the inlet gas flow passages 232 have a diameter ofapproximately 0.060 to 0.070 inches. FIG. 11 illustrates the gas flowfrom the passages 232 through the distribution grooves 234 with arrows242.

[0103] In a departure from previous embodiments, and as seen in FIG. 12,each of the spacers 206 is supplied with purge gas from one of the gasdistribution grooves 234 via a purge channel 244. These purge channelsare seen in cross-section in FIG. 14 and extend from the respective gasdistribution groove 234 directly to the spacer 206. In this manner, acontinuous supply of purge flow, indicated at 246, is supplied to theregions surrounding each spacer 206. Each of the spacers 206 fits withinan aperture 250 formed in the top surface of the recess 204. A clearanceis provided between the spacer 206 and its aperture 250 so that thepurge gas may flow upward therearound and protect the spacer fromdeposition gases. More particularly, when the wafer 248 is not present,the sweep gas through the outlets 214, 216 flows generally upward intothe reaction chamber, rather than outward around each of the spacers.This leaves the spacers 206 unprotected from etch or capping gases. Thespacer is defined by a lower cylindrical base 252 and upper elongatedcylindrical pin 254 having a rounded upper surface. The pin portion 254is undersized with respect to the aperture 250 to allow the purge flow246 therethrough. In one embodiment, the pin 254 has a diameter ofbetween 0.050 and 0.055 inches, while the aperture 250 has a diameter ofbetween 0.062 and 0.067 inches.

[0104] The present invention provides a susceptor combination enablingselection of different upper sections depending on the wafer size to beprocessed. Such a combination is especially useful in the reactionchamber 20 having the support plate 32. As mentioned above, thesusceptor preferably has a constant outer diameter to fit within thering 62, and aperture 33 in the support plate 32. As the upper sectiondefines the outer perimeter of the susceptor, it will by necessity havea constant diameter while the wafer recess varies in size to accommodatethe different wafer sizes. The bottom shape of each of the uppersections is designed to mate with a single lower section, which reducescosts somewhat. FIGS. 11-17 illustrate four different susceptorcombinations 200, 258, 278 and 300 for four different wafer sizes. Othersizes of wafers may of course be accommodated by such a combination, themaximum size only being limited by the outer diameter of the susceptor.

[0105]FIG. 15 illustrates a second version of a top section 260 of thewafer support system 200. The bottom section is the same as wasdescribed with respect to FIGS. 11-14. Indeed, an interface 262 betweenthe top section 260 and the bottom section 218 is the same as previouslydescribed, and the gas distribution grooves 234 in the bottom sectionare in the same location. The top section 250 differs from the earlierdescribed version by a reduced diameter recess 264. The recess 264 isdefined by the circular step 266, which in turn creates a larger radialdimension for the ledge 268. The top section 260 is adapted to supportsmaller sized wafers within the recess 264. In this respect, a pluralityof spacers 270 are positioned at 120□ intervals around the center of thesusceptor and at radial distances which provide adequate support forwafers of approximately 150 millimeters. To connect the purge gasgrooves 234 with the spacers 270, shortened purge channels 272 areprovided.

[0106]FIG. 16 illustrates a third version of a top section 280 of thewafer support system 200. Again, the bottom section is the same asbefore with the interface 282 between the top and bottom sections beingthe same. The top section 280 includes an enlarged ledge 284 terminatingin a circular step 286. The recess 288 thus formed is sized to receivewafers of approximately 125 millimeters in diameter. Purge channels 288lead to apertures surrounding the captured spacers 290 at radialdimensions sufficient to support the reduced-size wafers. It will benoted that the gas distribution grooves 234 extend radially outward fromthe recess 266, and then continue inward to the circular deliverygrooves.

[0107] In a fourth version of the top section 302, seen in FIG. 17, thestep 304 is even further moved inward, reducing the recess 306 to a sizesufficient to support 100 millimeter wafers. Again, the interface 308remains in the same location, as the bottom section of susceptor 300 isidentical to that previously described. The outer ledge 310 is greatlyenlarged in this embodiment. Three spacers 312 are provided at 120°intervals around the center of the susceptor, and three associated purgechannels 314 connect the gas distribution grooves 234 thereto. It willbe noted that the radial positions of the spacers 312 are within thecircle created by the three gas inlet apertures in the bottom surface ofthe susceptor. Indeed, the gas distribution grooves 234 extend radiallyoutward from the recess 306, and then continue inward to the circulardelivery grooves. Furthermore, the location of the support arm-receivingcavities is just outside of the recess 306, and is thus outside of thewafer when positioned on the susceptor 300. The ledge 310 surroundingthe recess 306 extends outward radially from the wafer for at least halfthe wafer diameter.

[0108] Referring now to FIGS. 21A-21E, there is illustrated anothervariation of a segmented susceptor. FIG. 21A illustrates a top section408 having a shallow recess 404 defined around its outer perimeter by acircular step 410 leading to a ledge 412 which forms the uppermostsurface of the susceptor. A circle of spaced sweep gas outlets 416 arelocated fairly close to the circular step 410. In the arrangement shown24 outlets are provided. Positioned closer yet to the step is a circleof circumferentially-spaced support pin or spacer holes 450. With thisarrangement, the wafer support pins or spacers will engage theundersurface of a wafer adjacent its outer periphery. Since a wafertypically has an alignment flat or notch on its outer periphery, sixsupport pins are provided instead of three as in the earlierarrangements. Thus, even if a wafer alignment flat or notch is alignedwith a support pin so that little or no support is provided by thatparticular pin, the wafer is still adequately supported by the otherfive.

[0109] As seen in FIG. 21B, a susceptor lower segment 418 includesshallow spider arm cavities 430, similar to those previously described.The cavities communicate with vertical gas flow passages 432 leading toa plurality of gas distribution grooves 434 formed in the upper surfaceof the bottom susceptor section 418. As seen in FIG. 21B, each gas flowpassage 432 communicates with groove sections which travel circuitouspaths leading to an outer annular groove 435 at circumferentially-spacedlocations. One segment of each path first extends radially outwardly andthen turns inwardly to form somewhat of a horseshoe shape, and thenextends circumferentially and radially outwardly to form a secondhorseshoe-shaped portion before intercepting the outer groove 435. Theother section of the path first extends radially inwardly and thencurves radially outwardly and then circumferentially before intersectingthe outer groove 435.

[0110] As seen from the fragmentary portion of the upper segment 408 inFIG. 21B and as further illustrated in FIGS. 21C, D, and E, the outergroove 435 is located beneath the circle of sweep gas outlets 416. Bypositioning the sweep holes so close to the outer periphery, the risk ofbackside deposition is greatly reduced. Further, the gas passages 434together with the increased number of gas outlets 216 increases thesweep gas flow volume. Also, reducing the spacing between the peripheryof the wafer and surrounding recess wall to about 0.10 inch furtherminimizes the possibility of deposition gas entering beneath the wafer.

[0111] By positioning the support pin cavities 430 adjacent the outerperiphery of the recess in the susceptor, the upper surface of the wafersupport pins 446 engage the lower surface of the outer periphery of awafer 448 in an outer area referred to as an exclusion zone 449. Thiszone does normally not become a part of a semi-conductor circuit chip.Hence, any slight marking to the undersurface of a wafer that might becaused by a support pin is inconsequential.

[0112]FIG. 21D illustrates a situation in which the wafer is formed withan alignment notch 451. Even with that arrangement a pin will engage thewafer if the notch should happen to be aligned with wafer, so long asthe wafer is centered and the gap between the wafer edge and thesurrounding recess is small. In fact, with a small enough gap, the pinwill engage the wafer even if not centered on the susceptor.

[0113]FIG. 21E illustrates the situation in which a wafer flat 453 isaligned with a support pin 446. As can be seen, the spacer pin is notactually engaging the wafer, but this is of no consequence since thewafer is supported by five other spacers.

[0114]FIGS. 22A and 22B, show another segmented susceptor assemblywherein a lower susceptor section 518 is shown with a circular groove537 which intersects three spider arm flow passages 532. A shallowannular recess 539 extends from the groove 537 out to a circular edge541 close to the periphery 518A of the lower section. More specifically,the edge 541 is located just radially beyond a circle ofcircumferentially-spaced sweep gas outlets 516 adjacent the periphery ofan upper susceptor segment 512, a fragment of which is shown in FIG.22A. Six support pins 546 are also conveniently shown in FIG. 22A. Thecircle of outlets 516 shown in the arrangement of FIGS. 22A and B isessentially the same as that shown in FIG. 21A except that three timesas many outlets are illustrated. Thus, in this arrangement, 72 outletsare utilized for a susceptor adapted to receive a 200 mm wafer 548. Theexact number of the outlets can of course be varied, but it isadvantageous having so many sweep gas outlets and having the shallow butlarge area annular recess 539 for feeding sweep gas to those outlets, asshown by the arrows in FIG. 22A. The increased gas flow greatly reducesthe risk of deposition gas reaching the backside of the wafer.

[0115]FIGS. 23A, B, and C, illustrate arrangement which can be similarto any of the arrangements previously described except that it employs aspacer in the form of a ring rather than a plurality of pins. Morespecifically, there is illustrated a thin generally flat spacer ring 615positioned in a shallow recess 604 in the top section 608 of a segmentedsusceptor 602. The outer perimeter of the ring 615 is located justwithin the edge of the recess as defined by a circular step 610 leadingto a ledge 612, which forms the upper surface of the susceptor. The ring615 extends inwardly to about the location occupied by the support pinsin the arrangement of FIGS. 21 and 22. As seen from FIG. 23B, the uppersurface 615 a of the ring 615 is not quite horizontal. Instead, itslopes or angles downwardly in a radially inward direction. Thus, theradially outer portion is the thickest vertically. The verticalthickness of the ring in the area engaged by the wafer is equal to theheight of the portion of support pins that protrude above the recess inthe upper section of the susceptor in the above-described arrangements.The wafer is effectively thermally decoupled from the susceptor andsuitably positioned with respect to the upper surface of the outer ledgeof the susceptor. With only the outer perimeter of the lower surface ofthe wafer 648 engaging the ring 615, the ring avoids or minimizes anymarkings on the backside of a wafer. Moreover, any insignificant effectwould be within the wafer exclusion zone and be confined to the edgeprofile of the wafer.

[0116] A plurality of radially extending passages or grooves 617 b areformed in the upper surface of the spacer ring 615. Thirty-two passagesare illustrated in a susceptor for receiving 200 mm wafers. As seen fromFIG. 23A, these passages are circumferentially-spaced and provideoutlets for the sweep gas, as shown by the arrows in FIG. 23B. The ringbody between and around those passages blocks deposition gas flow intothe backside of the wafer.

[0117]FIG. 23C illustrates a semi-circular cross-sectional shape of thepassage 615 b, but of course other configurations may be employed. Thecross-sectional area and the number of passages are selected to providethe desired flow, consistent with gas provided through passages 632 in alower susceptor section 618, seen in FIG. 23B. The passages 632 areshown for convenience in FIG. 23A even though no other details of alower susceptor section are shown. As mentioned above, any of the sweepgas arrangements described above may be employed with the ring conceptof FIGS. 23A-C. In fact, the support ring can be employed with uppersusceptor segments designed to receive support pins inasmuch as the pinholes do not interfere with the use of the ring and do not have asignificant effect on the sweep gas system. Thus, a user can employeither approach.

[0118] The ring can be conveniently made of the same material as thesupport pins or the susceptor.

[0119] In testing the wafer support system described above, it has beenlearned that certain aspects of the reactor system are particularlyimportant in obtaining satisfactory results. FIG. 18 illustrates arectangular chamber having a flat upper wall 324 and a flat lower wall325 in an inlet section and a flat lower wall 326 which is stepped downfrom the wall 325 by a flat vertical wall 327. The horizontal walls 324,325 and 326 are joined by flat vertical side walls 328 and 330 to createa chamber having a shallow rectangular inlet section and a deeperrectangular section adjacent to it in which is positioned a susceptor382 and a temperature compensation ring 362.

[0120] It is preferred that the ring 362 surrounding the susceptor havea generally rectangular exterior shape as shown in FIG. 19. Further, itis also desirable that the radiant heating lamp banks 351 and 352 aboveand below the upper and lower walls 324 and 326 of the quartz chamber inFIG. 18 define an exterior shape that is generally rectangular andconform to that of the ring, so that the projected radiant heat patternor column is likewise generally aligned with the ring. That is, the heatis primarily directed to the ring and the susceptor area rather thanbeing directed to the quartz walls adjacent the ring. This heatingarrangement is highly efficient and promotes uniform temperature anddeposition across the ring and the susceptor. Incidentally, the spotlamps 353 beneath the central portion of the susceptor are considered tobe part of the lower lamp bank 352.

[0121] The ring is supported on a suitable quartz stand 356 resting onthe bottom of the chamber. Alternate supporting arrangements may beemployed such as utilizing ledges or fingers extending from the adjacentquartz structure. This configuration of the ring and the radiant lampshas been found to work particularly well in a chamber having a generallyrectangular cross section formed by the flat upper and lower walls 324and 326 and vertical side walls 328 and 330.

[0122] The combination of the rectangular chamber and the rectangularring simplifies the process gas flow across the wafer. With therectangular ring, the process gas introduced through an injector such asat 46 in FIG. 1, is depleted generally uniformly across the width of thechamber such that the velocity profile of the process gas may begenerally uniform across the chamber as schematically indicated by thearrows 331 in FIG. 19. Consequently, a minimum of carrier gas isrequired with the rectangular ring and the rectangular chamber crosssection, since there is no need to increase flow in the center. Thereduced carrier gas flow means less cooling effect on the wafer. This isimportant for a wafer spaced from the susceptor, since the spaced waferis more responsive to the cool gas flow than is a wafer supporteddirectly on the susceptor. The volume of hydrogen gas has been reducedby about 75% in a prototype system. Stated differently, the ratio of thecarrier gas to the deposition gas has been reduced from a minimum ofabout 15 to 1 to a minimum of about 5 to 1.

[0123] With the wafer substantially thermally decoupled from thesusceptor, it has been found to be quite sensitive or responsive tononuniformity in the heat output of the lamp banks. For example, thespacing between the lamps and the distance of the lamp banks from thewafer and the susceptor 382 affect the uniformity of the heat patternobtained on the wafer. Thus, with the wafer spaced from the susceptor382, it has been found desirable to increase the distance between thewafer and the upper lamp bank 351 from that employed with a waferpositioned directly on the susceptor. Likewise, it has been founddesirable to increase the distance from the susceptor to the lower lampbank 352. But it has been found desirable to increase the space betweenthe wafer and the upper lamp bank 351 more than the space between thelower lamp bank 352 and the susceptor.

[0124] Common to all the various arrangements disclosed, the wafer issupported in a reactor largely thermally decoupled from the susceptor.That is, the wafer is supported on spacers or pins that space the wafera substantial distance above the susceptor. The pins have minimalcontact with the wafer. The sweep gas is preheated by way of the novelsusceptor design so that it has an insignificant effect on thetemperature of the wafer but yet effectively prevents process gases fromdepositing on the backside of the wafer. Since the wafer is essentiallydecoupled from the susceptor, the wafer can heat more quickly ascompared to a system wherein the wafer is in contact with the susceptor.

[0125] The lamp banks 351 and 352 are controlled by a suitableelectronic controller schematically shown at 390 in FIG. 18. Thecontroller includes a transmitter component that receives signals fromthe temperature sensors in the ring surrounding the susceptor and fromthe sensor located at the center of the lower side of the susceptor.These temperature signals are transmitted to heater control circuitry.Additionally, temperature control information such as varioustemperatures settings desired for a particular deposition cycle isinputted to the heater control circuitry. That information is thenprocessed by the control circuitry, which generates control signals thatcontrol power to the heating assemblies. Further details of such asystem, are disclosed in U.S. Pat. No. 4,836,138, which is expresslyincorporated herein by reference.

[0126] In that earlier system, some lamps from the upper and lower lampbanks are controlled together as a zone that would be adjusted as aunit. That is, the power ratio was fixed so that if the power wasincreased to a lamp in the upper bank, a corresponding power increasewas provided to a lamp of that particular zone in the lower bank aswell. The ratio is advantageously fixed by applying the temperaturecontrol signal for a given lamp bank through a pre set ratiopotentiometer that modifies the control signal before it is applied tothe lamp bank. The other lamp banks advantageously have their controlsignals modified using similar ratio control circuitry, there byproviding a pre set power ratio between the lamp banks within a zone. Inthis way the various zones can be adjusted independently. One change tothe system described in U.S. Pat. No. 4,838,138 has been made as aresult of the wafer on spacers design. An analog ratio control has beenadded to the circuitry to permit the lamp bank power ratio between theupper and lower lamps of a particular heating zone to be adjusted atvarious points during the process as a result of the thermal decouplingof the wafer from the susceptor. This is advantageously accomplished inthe current system by adding a dynamically controllable ratiopotentiometer in series with the pre set ratio potentiometer for thelamps in the upper lamp bank within a zone. Thus, the control signal forthe upper lamp bank within the zone may be changed using the dynamicallycontrollable potentiometer. Because the total power applied to the lampsin that zone remains about the same, when the power to the upper banklamps within the zone is changed, the power to the corresponding lamps352 in the lower bank is changed in the opposite direction. Thus thepower ratio between the two is changed. This enables the temperature ofthe susceptor and the wafer to be maintained close together even thoughthey are physically spaced.

[0127] Referring more specifically to the heating system disclosed inU.S. Pat. No. 4,838,138, lamps 48B and 48C of FIG. 6 form a centralheating portion of an upper lamp bank, and the lamps 78B and 78C form acentral portion of a lower bank. The ratio of power between the upperand lower banks was changed utilizing the analog ratio control bychanging the power applied to the upper bank lamps 48B and 48C, whilethe total power applied to the lamps 78B, 78C, 48B and 48C remains aboutthe same. This results in a change to the power to the lower bank in theopposite direction.

[0128] An example of utilizing the analog ratio control is illustratedin the graph of FIG. 20. The solid line illustrates a time temperaturerecipe for the processing of a semi-conductor wafer. The solid lineindicates a wafer being loaded into a reactor with the lamps set toprovide a starting temperature of 900° C. The temperature is maintainedat that level for about 30 seconds. Additional heat is then appliedramping the temperature up to about 1150° C. in about 70 seconds. Thewafer is then subjected to a bake or etch step at that level for about aminute. The temperature is then allowed to decrease to a depositiontemperature of about 1050° C. with the cooling occurring in about 30seconds. The temperature is maintained at 1050° C. for about 70 secondsin a predeposition phase followed by about 70 seconds while thedeposition is occurring on the wafer. The wafer is then allowed to coolto about 900° C. for a similar time. The cycle is then complete and thewafer is removed at the 900° C. level.

[0129] As explained above, the ratio of the heat between an upper bankof lamps and a lower bank of lamps has been kept at a predeterminedratio when the wafer being processed is supported directly on thesusceptor. That method is satisfactory with the wafer positioned on thesusceptor inasmuch as the temperature between the susceptor and thewafer are largely the same throughout the cycle. However, with the waferspaced above the susceptor, it is desirable to change the ratios betweenthe upper and lower heating banks in the central portion of the waferduring the cycle. The broken line of FIG. 20 provides an example of theanalog ratio control. The ratio percentage change is illustrated on theright-hand scale of the chart of FIG. 20. At the start of the cycle, theratio is shown at a zero percentage variation, meaning that the lampsare at what might be termed a steady state condition or the fixed ratioposition. This does not mean that the power between the upper and lowerbanks is necessarily the same. As an example of an operating system theupper lamps received about 48% of the power and the lower lamps about52%. With a wafer supported in direct contact with a susceptor, thepower ratio would simply remain on the zero or steady state line.However, that is not satisfactory with the wafer spaced from thesusceptor.

[0130] It is desirable to maintain the temperature between the wafer andthe susceptor approximately the same during the heating cycle. Since thewafer is spaced above the susceptor and has less mass than thesusceptor, it heats more quickly then the susceptor. Thus, thepercentage of heat required by the wafer is reduced during the phase ofthe cycle in which the temperature is ramped up from 900° C. to 1150° C.Thus, the broken line of the graph shows that the percentage of powerapplied to the upper lamps is decreased to a ratio about 20% below thesteady state or zero change condition. As mentioned above, the totalpower applied to the lamps is about the same as it would be if the ratiowere not changed, and hence, this results in an increase in thepercentage of the power being applied to the lower lamps. With thischanged ratio, the temperature of the wafer and the susceptor remainsubstantially the same as the temperature is ramped up to the 1150° C.level. While the temperature is maintained at that level for the bake oretch phase, the variable ratio control is returned to the zero or steadystate ratio as shown on the graph.

[0131] When it is then desirable to cool the wafer from 1150 to 1050°C., the power is reduced; but some power is continued to control thecooling. Since the wafer spaced from the susceptor cools more quicklythan the susceptor, the ratio between the upper and lower lamps ischanged by reducing the power to the upper lamps a lesser percentagethan to the lower lamp to maintain the wafer at the susceptortemperature. As shown on the broken line, the percentage of power to theupper lamp is increased so that the ratio is increased by about 20% tothe upper lamp. While the wafer is maintained at that 1050° C. level,the power ratio is returned to the steady state condition so that at thetime that the predeposition phase is over and the deposition phase is tocommence, the power ratio is at the so-called steady state condition.After deposition, it is desirable to allow the wafer to cool to the 800°C. level; and hence again, the ratio is changed by increasing thepercentage of the power to the upper lamps by about 20%. When the 800°C. level is reached, the power percentage is decreased with respect tothe upper lamp, allowing the ratio to return to its steady statecondition. It should be kept in mind that the total power applied isapproximately the same and it is only the power ratio between the upperand lower banks which is being altered. The actual percentage changes,of course, have to be determined for the particular wafers beingprocessed and the particular temperatures and processes involved. Theanalog ratio control feature employs multiplier circuits to modify thepower signal to the upper lamps by the appropriate fraction to obtainthe desired result.

[0132]FIGS. 24 and 25 illustrate an arrangement similar to that in FIGS.23A, B and C, but it includes a spacer ring 715 having a configurationdifferent from the spacer ring 615. Instead of being a flat ring with aplurality of circumferentially spaced grooves 615 b in its uppersurface, the ring 715 includes a central main body portion 715 b havinga generally flat rectangular cross-section, as best seen in FIG. 25B. Aplurality of lands, lips or projections 715 a extend upwardly from themain body portion 715 b to form spacers for the substrate. In thearrangement shown in FIG. 24, six such lands are provided,circumferentially spaced at an equal angle α of approximately 60°. Asseen from FIG. 25A, the lands extend the complete radial thickness ofthe ring, but the upper surface of the land 25 b is slightly sloped froma radially outer edge to a lower radially inner edge of the ring. Thisarrangement minimizes the contact between the substrate 648 to a veryslight line contact at the six land locations. Further, as can be seenfrom FIG. 25, the circumferential width of the land is very small,preferably only about 0.030 of an inch. The slope of the upper surfaceof the land is only about 2° from horizontal. Projections orprotuberances with other configurations can be employed instead of thelands.

[0133] The ring 715 is further provided with a plurality of feet 715 cdepending from the main body portion 715 b at circumferentially spacedintervals. More specifically, it can be seen from FIG. 24 that a pair ofsuch legs straddle a land 715 a and are spaced from the land acircumferential angle β of about 10°. This creates a total of 12 feet,two adjacent each side of each land 715 a. As seen from FIGS. 25A, 25Band 25C, the feet extend the full width of the main ring body 715 a,except that the outer lower corners of the feet 715 c are chamfered.

[0134] Spacers supporting a wafer above a susceptor have less resistanceto thermal transport than the gas between the wafer and the susceptor.Thus, undesirable thermal gradients can be created within the wafer nearthe contact area. This is most significant with larger thermal gradientsthat may occur during rapid heat ramp-up of the system. An advantage ofhaving a land 715 a circumferentially spaced from a foot 715 c is thatthe thermal path between the susceptor and the wafer is much longer thanthat with a spacer extending directly between the two components. Or,stated differently, the thermal path from the bottom of one foot to thetop of an adjacent land is much greater than the height of the ringincluding the foot and the land. This in turn permits rapid heating of asystem, which of course improves productivity.

[0135] With the arrangement illustrated in FIGS. 24 and 25, theremainder of the susceptor can be formed utilizing any of the susceptorconfigurations of FIGS. 2-17, with or without spacer pins. That is, ifthe spacer ring is provided with a height equal to that of the spacerpins, the spacer pins need not be employed. Alternatively, the totalheight of the blocker or spacer ring can be slightly less than that ofthe spacer pins such that the substrate is supported by the spacer pins.

[0136] Various dimensions of the spacer ring 715 may be employed. Forexample, the height A of the land 715 a in one prototype version for an8 inch wafer is approximately 0.022 of an inch, with the central bodyportion being about 0.035 of an inch, and the feet being about 0.020 ofan inch, for a total of about 0.077 of an inch. The thickness B of thecentral body portion 715 b can be increased to decrease the area of thepassages between the lands and between the feet. In anotherconfiguration, the main body portion 715 b is about 0.045, with theprojection 715 a being about 0.017 and the foot being about 0.015. Itshould be noted that since the diameter of the substrate is slightlyless than the outer diameter of the ring, the height of the land 715 aat the area contacted by the periphery of the substrate is about thesame as the height of the foot. In another configuration, the centralbody portion 715 b is about 0.055 of an inch, with the upper and lowerportions being about 0.010 of an inch each. In yet a fourthconfiguration, the central body portion was about 0.065 of an inch, withthe upper and lower projections being only about 0.005. Thus, it can beseen by varying the dimensions of the ring, the cross-sectional area ofthe passages between the ring and the substrate, and the ring and thesusceptor, are correspondingly varied.

[0137]FIGS. 26 and 27 illustrate another configuration of a spacer orblocker ring 815. As seen from FIGS. 26, 27, 27A and 27B, the ringincludes a main body portion 815 b having a generally rectangularcross-section, and includes an upwardly extending continuous annular rib815 a which is positioned approximately midway between inner and outerdiameters of the ring. The ring is further provided with a plurality ofcircumferentially spaced feet 815 c that depend from the main bodyportion 815 b. These feet are approximately the same as the feet 715 cillustrated in FIG. 25. That is, in the arrangement illustrated, a pairof feet 815 c are spaced from each other at an approximate angle 0 ofabout 20°. Further, there are six pairs of such feet circumferentiallyspaced approximately 60°, thereby creating a total of 12 feet.

[0138] The ring 815 is preferably used as a blocker ring in which theoverall height of the ring is less than that of the support pins orspacers discussed above, so that the substrate is supported on thespacer pins rather than the blocker ring. In that sense, the ring 815serves only to block the inward flow of deposition gas and to furtherimprove the action of the sweep or purge gas by providing a thin annularpassage or slit of only about 0.010 of an inch between the upper edge ofthe rib 815 a. Also provided are circumferentially spaced, verticallyshort passages between the feet 815 c. In a preferred arrangement, theheight A¹ of the rib 815 a is about 0.025 of an inch, the main bodyheight B¹ is about 0.030 of an inch, and the height C¹ of the foot isabout 0.010 of an inch for a total of about 0.065. When used with spacerpins that create a gap of 0.075 inch, this created the 0.010 inchpassage between the rib and the substrate.

[0139] The radial dimension or width of the annular rib 815 a ispreferably about 0.025 inch; and as seen in FIG. 27B, it has a generallyflat central portion with rounded shoulders.

[0140] To further block the gap between the substrate and the susceptor,the blocker ring feet 815 c may be eliminated, creating a cross-sectionillustrated in FIG. 27C, wherein the main body portion is about 0.040inch.

[0141]FIG. 28 shows a blocker ring 915 having a cross section similar tothe ring 815 accept that an annular rib 915 a is located adjacent theinner diameter of the ring, thus giving the ring cross section somewhatof an L shape, with the radial dimension of the ring representing thelong leg of the L shape and the upwardly extending rib representing theshorter leg.

[0142] An advantage of the arrangement illustrated in FIGS. 26, 27, and28 is that with the ribs 815 a and 915 a spaced from the substrate, thering is substantially thermally decoupled from the susceptor so thatthere are no significant temperature discontinuities in the area of thesusceptor above the ring that might create slip. At the same time, sincea substantial portion of the gap is blocked by the ring, deposition gasis blocked from entering the area beneath the substrate. Related to thatis the fact that the velocity of the sweep gas is increased as it passesby the ring, which further inhibits the flow of deposition gas beneaththe substrate. The input gas flow into the gap from the passages throughthe support spider can be controlled to create the desired flow and apressure is maintained in the gap between the susceptor and thesubstrate that is greater than the pressure above the substrate. Thispressure differential, of course, maintains the flow of purge gas orsweep gas and prevents the flow of deposition gas on the backside of thesubstrate. The use of a blocker ring, such as in FIGS. 23-28, providesgood backside protection for the wafer with less gas flow than withoutthe ring. Gas flow at various low flow rates has provided good results.

[0143] While some of the spacer rings are described as having feet orlegs projecting downwardly from a main body portion, the susceptor couldbe provided with lips or bumps in those areas to create passages withthe ring being flat or having feet. Similarly, while it is mostpractical to have a space ring or spacer legs formed separately from thesusceptor, similar structures could be formed integral with thesusceptor.

[0144] Also, while the completely ring shaped blockers discussed aboveare the currently preferred shape, blocker that does not extendcompletely to a closed 360° shape would be utilized. Similarly, a ringcould be made as two or more separate pieces that could substantiallyform a ring would be useful. In addition a blocker not completelycircular could be used. Other such changes are also included to comewithin the scope of the appended claims.

[0145] Although this invention has been described in terms of certainpreferred embodiments, other embodiments are also within the scope ofthis invention. For example, although some of the illustratedembodiments are described for specific sizes of wafers, the samefeatures may also be used to accommodate larger wafers. Indeed, wafersof 300 mm or larger are presently contemplated to supplement traditional200 mm and smaller sized wafers. With larger wafers it may be desirableto employ additional spacers in a ring spaced radially inwardly from thethree spacers 100 shown in FIG. 18, and offset circumferentially to bebetween the spacers of FIG. 18.

1-112 (Canceled)
 113. A method of supporting a semiconductor wafer,comprising: supporting a wafer on a susceptor; permitting gas to flowthrough the susceptor between regions above and below the susceptor;supporting the susceptor on a plurality of support arms that extendgenerally radially outward and upward from an upper section of asubstantially vertical shaft, a central vertical axis of the shaft beingaligned with a central vertical axis of the susceptor, the arms engagingthe susceptor such that rotation of the shaft about the central verticalaxis of the shaft causes the susceptor to rotate about the centralvertical axis of the susceptor; and rotating the shaft about the centralvertical axis of the shaft.
 114. The method of claim 113, furthercomprising providing radiant energy to the wafer and susceptor.
 115. Themethod of claim 113, wherein the support arms and the shaft aretransparent to radiant energy.
 116. The method of claim 113, whereinsupporting the wafer on the susceptor comprises supporting the wafer ona plurality of spacers extending upwardly from an upper surface of thesusceptor, such that the wafer is slightly spaced from the uppersurface.
 117. The method of claim 113, wherein permitting gas to flowthrough the susceptor comprises permitting gas to flow through one ormore gas flow passages in the susceptor, each of the one or morepassages having an upper opening at an upper surface of the susceptorand a lower opening at a lower surface of the susceptor.
 118. The methodof claim 117, wherein the one or more passages include horizontalchannels inside the susceptor.
 119. The method of claim 113, whereinsupporting the susceptor comprises inserting upper ends of the supportarms into cavities within a lower surface of the susceptor, each of thecavities positioned along a circle centered on the central vertical axisof the shaft.